1. Field of the Invention
The present invention concerns a plant for making continuous elastic yarns of silicone material usable in the medical field, that of protective technical fabrics and in those industrial fields for which elastic yarns are required with a section of less than 0.7 mm, advantageously 0.3-0.4 mm, and even as little as 0.2-0.1 mm, resistant to certain chemical agents and/or to high or low temperatures, and in particular cases usable as electric conductors. In particular, the present invention can be used to make so-called elastic yarns of silicone rubber.
The present invention also concerns the continuous elastic yarn obtained using the plant.
Here and hereafter in the description and claims, the term elastic yarn means generally a continuous extruded product, either filiform or with a different profile, for example packings, with a count higher than a bead, filament, thread or profile, that is, the multi-filament type.
2. Description of Related Art
Plants are known, for the extrusion of silicone material used to make extruded products of various section and thickness.
Known plants normally extend horizontally and comprise, in succession, feed means that feed the material in the form of paste, an extrusion station, in which the extruded product is made, and a vulcanization station.
This type of known plant has the disadvantage that the extruded product, at the end of the extrusion process, is deposited on a conveyor belt or strip that normally advances at a speed substantially equal to the speed of extrusion.
Since this feed occurs horizontally, or substantially horizontally, the extruded product being made is affected both by the extrusion pressure and also the force of gravity, under the action of which the extruded product tends to modify its section, flattening before entering the vulcanization station, so that, at entrance to the vulcanization station, the extruded product no longer has the correct section but is deformed, mainly due to the extrusion pressure.
This problem is accentuated when the extruded products to be made are particularly fine, for example in the case of silicone based elastic yarns with a diameter of less than 0.7 millimeters, to as little as 0.2 and 0.1 mm.
This problem also makes it very difficult to have a precise control on the value of section obtained, and also it does not allow to guarantee a uniform section over the length of the yarn.
Moreover, known plants do not allow to extrude materials such as silicone rubber, with a reduced section and in the liquid state, or at least not totally solid, because the elastic yarn exiting from the extrusion station would not be firm enough to be deposited on a conveyor belt or to be held by clamping means and drawn through the vulcanization station.
Another disadvantage of known plants is that the type of oven usually used in the vulcanization station are normally moved manually on each occasion, to be moved closer to or away from the vulcanization station, depending on the type of extruded product to be processed, but this interrupts the production process and increases both the economic cost and the production times, and also does not guarantee precision positioning.
Known solutions for producing extruded products made of silicone material work on thicknesses having a slightly larger size than those sought in the present invention, such as for example DE-C2-38 44 60.
Other solutions work on products in which the field of use is completely different from the production of elastic yarns according to the present patent application, such as DE-A1-101 45 945, which concerns the production of multi-layer optical cables, or W-A1-2008/074622, which concerns the production of windscreen wiper brushes, that is, with values of size and quality that cannot be compared with those required in continuous elastic yarns which are the object of the present patent application.
Purpose of the present invention is to achieve a plant for the continuous production of elastic yarns made of silicone material that overcomes the shortcomings of the state of the art and allows to make elastic yarns, simply and economically, with a section of much less than 0.7 mm, advantageously less than 0.4 mm and even 0.2-0.1 mm.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.